An epidemiologic link between depression and cardiovascular disease is well documented. Depression can be both a causative factor in the development of cardiovascular disease as well as a result of its development. Ironically, the development of cardiovascular disease is often likely to result in additional depressive symptoms in patients as the level of worry about their health increases, thus creating a vicious circle. Psychiatric disturbances such as severe depression have been reported in many patients receiving implantable cardioverter/defibrillators (ICDs). Approximately 65% of post-MI patients and up to 87% of ICD recipients reportedly have symptoms of mild or severe depression. Depression in patients with heart disease also has a clear effect on patient prognosis. It is well documented that heart failure patients, post-CABG patients and post-MI patients have a worsened prognosis if they have concomitant depression, including an increased risk for subsequent cardiac events such as re-hospitalizations and re-infarction. The worsening prognosis associated with depression is also consistent in other types of cardiovascular disease including unstable angina, CAD and heart failure. Post-CABG patients have been shown to not only have an increased risk of mortality, readmissions and cardiac events, but also to have a reduction in functional improvement post surgery. Clearly, breaking the vicious circle of cardiovascular disease and depression could have a significant impact on slowing the progression and clinical outcome of cardiovascular diseases in a significant number of patients. Depression has also been shown to be an important causative factor in many other diseases. A device based system for detection, signaling and potential treatment of depression, could significantly improve morbidity and mortality in these patients.